/**
 * UTF16和UTF8转换对照表
 * U+00000000 – U+0000007F 	0xxxxxxx
 * U+00000080 – U+000007FF 	110xxxxx 10xxxxxx
 * U+00000800 – U+0000FFFF 	1110xxxx 10xxxxxx 10xxxxxx
 * U+00010000 – U+001FFFFF 	11110xxx 10xxxxxx 10xxxxxx 10xxxxxx
 * U+00200000 – U+03FFFFFF 	111110xx 10xxxxxx 10xxxxxx 10xxxxxx 10xxxxxx
 * U+04000000 – U+7FFFFFFF 	1111110x 10xxxxxx 10xxxxxx 10xxxxxx 10xxxxxx 10xxxxxx
 */
//外部js引用时这样写：import {Base64} from '/xxx/base64';//路径需要根据实际路径去写
export let Base64 = {
  // 转码表
  tables: [
    'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H',
    'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P',
    'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X',
    'Y', 'Z', 'a', 'b', 'c', 'd', 'e', 'f',
    'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n',
    'o', 'p', 'q', 'r', 's', 't', 'u', 'v',
    'w', 'x', 'y', 'z', '0', '1', '2', '3',
    '4', '5', '6', '7', '8', '9', '+', '/'
  ],
  UTF16ToUTF8: function (str) {
    let results = [],
      len = str.length;
    for (let i = 0; i < len; i++) {
      let code = str.charCodeAt(i);
      if (code > 0x0000 && code <= 0x007F) {
        /* 一字节，不考虑0x0000，因为是空字节
           U+00000000 – U+0000007F 	0xxxxxxx
        */
        results.push(str.charAt(i));
      } else if (code >= 0x0080 && code <= 0x07FF) {
        /* 二字节
           U+00000080 – U+000007FF 	110xxxxx 10xxxxxx
           110xxxxx
        */
        let byte1 = 0xC0 | ((code >> 6) & 0x1F);
        // 10xxxxxx
        let byte2 = 0x80 | (code & 0x3F);
        results.push(
          String.fromCharCode(byte1),
          String.fromCharCode(byte2)
        );
      } else if (code >= 0x0800 && code <= 0xFFFF) {
        /* 三字节
           U+00000800 – U+0000FFFF 	1110xxxx 10xxxxxx 10xxxxxx
           1110xxxx
        */
        let byte1 = 0xE0 | ((code >> 12) & 0x0F);
        // 10xxxxxx
        let byte2 = 0x80 | ((code >> 6) & 0x3F);
        // 10xxxxxx
        let byte3 = 0x80 | (code & 0x3F);
        results.push(
          String.fromCharCode(byte1),
          String.fromCharCode(byte2),
          String.fromCharCode(byte3)
        );
      } else if (code >= 0x00010000 && code <= 0x001FFFFF) {
        // 四字节
        // U+00010000 – U+001FFFFF 	11110xxx 10xxxxxx 10xxxxxx 10xxxxxx
      } else if (code >= 0x00200000 && code <= 0x03FFFFFF) {
        // 五字节
        // U+00200000 – U+03FFFFFF 	111110xx 10xxxxxx 10xxxxxx 10xxxxxx 10xxxxxx
      } else /** if (code >= 0x04000000 && code <= 0x7FFFFFFF)*/ {
        // 六字节
        // U+04000000 – U+7FFFFFFF 	1111110x 10xxxxxx 10xxxxxx 10xxxxxx 10xxxxxx 10xxxxxx
      }
    }

    return results.join('');
  },
  UTF8ToUTF16: function (str) {
    let results = [],
      len = str.length;
    let i = 0;
    for (let i = 0; i < len; i++) {
      let code = str.charCodeAt(i);
      // 第一字节判断
      if (((code >> 7) & 0xFF) == 0x0) {
        // 一字节
        // 0xxxxxxx
        results.push(str.charAt(i));
      } else if (((code >> 5) & 0xFF) == 0x6) {
        // 二字节
        // 110xxxxx 10xxxxxx
        let code2 = str.charCodeAt(++i);
        let byte1 = (code & 0x1F) << 6;
        let byte2 = code2 & 0x3F;
        let utf16 = byte1 | byte2;
        results.push(Sting.fromCharCode(utf16));
      } else if (((code >> 4) & 0xFF) == 0xE) {
        // 三字节
        // 1110xxxx 10xxxxxx 10xxxxxx
        let code2 = str.charCodeAt(++i);
        let code3 = str.charCodeAt(++i);
        let byte1 = (code << 4) | ((code2 >> 2) & 0x0F);
        let byte2 = ((code2 & 0x03) << 6) | (code3 & 0x3F);
        let utf16 = ((byte1 & 0x00FF) << 8) | byte2
        results.push(String.fromCharCode(utf16));
      } else if (((code >> 3) & 0xFF) == 0x1E) {
        // 四字节
        // 11110xxx 10xxxxxx 10xxxxxx 10xxxxxx
      } else if (((code >> 2) & 0xFF) == 0x3E) {
        // 五字节
        // 111110xx 10xxxxxx 10xxxxxx 10xxxxxx 10xxxxxx
      } else /** if (((code >> 1) & 0xFF) == 0x7E)*/ {
        // 六字节
        // 1111110x 10xxxxxx 10xxxxxx 10xxxxxx 10xxxxxx 10xxxxxx
      }
    }

    return results.join('');
  },
  encode: function (str) {
    if (!str) {
      return '';
    }
    let utf8 = this.UTF16ToUTF8(str); // 转成UTF-8
    let i = 0; // 遍历索引
    let len = utf8.length;
    let results = [];
    while (i < len) {
      let c1 = utf8.charCodeAt(i++) & 0xFF;
      results.push(this.tables[c1 >> 2]);
      // 补2个=
      if (i == len) {
        results.push(this.tables[(c1 & 0x3) << 4]);
        results.push('==');
        break;
      }
      let c2 = utf8.charCodeAt(i++);
      // 补1个=
      if (i == len) {
        results.push(this.tables[((c1 & 0x3) << 4) | ((c2 >> 4) & 0x0F)]);
        results.push(this.tables[(c2 & 0x0F) << 2]);
        results.push('=');
        break;
      }
      let c3 = utf8.charCodeAt(i++);
      results.push(this.tables[((c1 & 0x3) << 4) | ((c2 >> 4) & 0x0F)]);
      results.push(this.tables[((c2 & 0x0F) << 2) | ((c3 & 0xC0) >> 6)]);
      results.push(this.tables[c3 & 0x3F]);
    }

    return results.join('');
  },
  decode: function (str) {
    //判断是否为空
    if (!str) {
      return '';
    }

    let len = str.length;
    let i = 0;
    let results = [];
    //循环解出字符数组
    while (i < len) {
      let code1 = this.tables.indexOf(str.charAt(i++));
      let code2 = this.tables.indexOf(str.charAt(i++));
      let code3 = this.tables.indexOf(str.charAt(i++));
      let code4 = this.tables.indexOf(str.charAt(i++));

      let c1 = (code1 << 2) | (code2 >> 4);
      results.push(String.fromCharCode(c1));

      if (code3 != -1) {
        let c2 = ((code2 & 0xF) << 4) | (code3 >> 2);
        results.push(String.fromCharCode(c2));
      }
      if (code4 != -1) {
        let c3 = ((code3 & 0x3) << 6) | code4;
        results.push(String.fromCharCode(c3));
      }

    }

    return this.UTF8ToUTF16(results.join(''));
  }
};